US4370667A - Laser recorder - Google Patents

Laser recorder Download PDF

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Publication number
US4370667A
US4370667A US06/231,561 US23156181A US4370667A US 4370667 A US4370667 A US 4370667A US 23156181 A US23156181 A US 23156181A US 4370667 A US4370667 A US 4370667A
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Prior art keywords
output
input
coupled
signal
high frequency
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US06/231,561
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English (en)
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Yuji Ohara
Masahiro Ohnishi
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Fujifilm Holdings Corp
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Fuji Photo Film Co Ltd
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Assigned to FUJI PHOTO FILM CO LTD. reassignment FUJI PHOTO FILM CO LTD. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: OHARA, YUJI, OHNISHI, MASAHIRO
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/405—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
    • H04N1/4055—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern
    • H04N1/4056—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern the pattern varying in one dimension only, e.g. dash length, pulse width modulation [PWM]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits

Definitions

  • the present invention relates to a recorder having a semiconductor laser which can reproduce with densities of more than several tens of levels a picture such as a photograph having halftones.
  • a picture having halftones can be recorded by various techniques by which a laser beam is intensity-modulated.
  • an ultrasonic optical modulator is employed;
  • the discharge current of a gas laser is changed, and
  • the current of a semiconductor laser is varied.
  • the first technique requires an expensive ultrasonic optical modulator and a fine adjustment device for setting the modulator to the Bragg angle.
  • the first technique is disadvantageous in that the device has a high manufacturing cost and intricate construction.
  • the gas laser discharge current modulation of the second technique suffers from drawbacks in that its modulation frequency range is very low, only several hundreds of Hertz, and the service life of the laser tube is reduced because the discharge current is varied.
  • the third technique in which the current of the semiconductor laser is varied is also disadvantageous in that, since the semiconductor laser has an optical output current characteristic as indicated in FIG. 1, the optical output is greatly changed by changing the current only slightly, and accordingly it is considerably difficult to modulate the optical output by more than several tens of levels by changing the current.
  • a further object of the invention is to provide a laser recorder which can record a picture rich in halftones.
  • a laser recorder using a semiconductor laser which utilizes the high frequency modulation characteristic of the semiconductor laser to provide more than several hundreds of modulation levels.
  • the invention provides an improved quality of an image recorded by a laser recorder device such as that disclosed in U.S. application Ser. No. 214,815 filed Dec. 9, 1980 (corresponding to Japanese Patent Application No. 168565/79 filed Dec. 25, 1979) filed by the present applicant.
  • a laser recorder device such as that disclosed in U.S. application Ser. No. 214,815 filed Dec. 9, 1980 (corresponding to Japanese Patent Application No. 168565/79 filed Dec. 25, 1979) filed by the present applicant.
  • a sampling pulse whose frequency is higher by at least two orders of magnitude than that of the sampling pulse is applied to a semiconductor laser with the frequency of the high frequency pulse signal being controlled according to the input signal.
  • a specific feature of the invention resides in that, in the laser recorder device described above, two sampling pulses of different phases are alternately employed for every scanning line.
  • sampling pulse is a pulse signal for sampling an input video signal at predetermined time intervals.
  • the frequency of the sampling pulse can be selected as desired. However, it is preferable, in order to reproduce a picture with a high resolution, that the frequency be slightly higher than the highest frequency of the video signal.
  • the term "high frequency pulse” is a pulse whose frequency is higher than that of the sampling pulse, preferably several hundreds to several ten thousands times higher. Both pulses may be generated separately although it is preferable to generate the sampling pulse by frequency-dividing the high frequency pulse as described later with reference to a preferred embodiment of the invention.
  • the number of high frequency pulses N does not correspond linearly to the input signal but also takes into consideration a logarithmic conversion relation and a recording material characteristic or an input/output characteristic which has been stored in advance.
  • input signal is a video signal although it may be an analog signal or a digital signal as well.
  • FIG. 1 is a graphical representation indicating a current-light emission characteristic of a semiconductor laser
  • FIG. 2 is a graphical representation indicating pulse numbers controlling a semiconductor laser with recorded image densities
  • FIGS. 3 and 4 are block diagrams showing a preferred embodiment of a laser recorder constructed according to the invention.
  • FIGS. 5, 6 and 7 are timing charts showing various signals in the laser recorder according to the invention.
  • FIGS. 8A-8E taken together, are explanatory diagrams for a description of an image recorded by the laser recorder of the invention.
  • FIG. 2 is a graphical representation indicating the above-described relation in the case where the data ⁇ (the gradient of the characteristic curve) of a recording material is 1 and the highest density is 2.0.
  • the intensity modulation is carried out with about 100 pulses, the density difference D changes by about 0.2 for each pulse while the density difference D changes only by about 0.1 for each pulse in the vicinity of about 20 pulses in the high density range. That is, in the case of FIG. 2, the gradations of low density are reproduced very coarsely. In order to reproduce more density levels, the sampling must be so performed that intensity modulation is carried out with the maximum number of pulses being 1000 or more.
  • a semiconductor laser can be pulse-modulated at high rate.
  • the modulation high rate characteristic of a semiconductor laser is utilized to perform pulse modulation with a high frequency signal wherein the semiconductor laser beam is intensity-modulated with a high frequency signal higher in frequency by two or three orders of magnitude than the highest frequency of the input video signal to thereby accurately reproduce halftones on a recording sheet.
  • FIG. 3 is a block diagram of a first preferred embodiment of a laser recorder according to the invention.
  • the laser recorder includes a semiconductor laser 1, a beam shaping lens 2, a deflector 3, a focusing lens 4, and a recording sheet 5.
  • the recording sheet be a silver salt photographic sheet or a xerographic sheet which can reproduce halftones and is sensitive to the red or infrared wavelength of a semiconductor laser beam.
  • the semiconductor laser beam 6 is collimated by the beam shaping lens 2, deflected by the deflector 3, and formed into a spot having a predetermined size by the focusing lens 4 to carry out a main scanning operation over the recording sheet 5 to form a scanning line 7.
  • the auxiliary scanning of the laser beam is carried out by moving the recording sheet 5 in the direction of the arrow 8.
  • the deflector 3 is a galvanometer.
  • a feature of the semiconductor laser is that it can be modulated with a pulse signal of a high frequency up to several hundreds of megahertz.
  • the quantity of light can be controlled by the number of pulses applied. For instance, if in the case where the highest video frequency is 10 KHz, a video signal sampled with 10 KHz pulses is pulse-modulated with a 10 MHz signal and the number of output pulses is controlled accordingly, modulation can be achieved with the number of pulses applied ranging from zero to several thousands according to the variations in magnitude of the video signal whereby accurate halftone modulation can be achieved.
  • the amplitude of an input video signal 9 is amplified to a predetermined level by a waveform shaping amplifier 10.
  • the video signal is a received facsimile signal.
  • a high frequency oscillator 11 outputs a high frequency pulse signal 12 which is applied to a sampling pulse generating circuit 13 which in turn outputs a sampling pulse signal 14.
  • the detailed construction of the sampling pulse generating circuit 13 will be described later.
  • the frequency of the high frequency pulse signal 12 is 25 MHz and the frequency of the sampling pulse signal 14 is 25 KHz, for instance.
  • the frequencies of the high frequency pulse signal 12 and the sampling pulse signal 14 are determined from the highest video frequency of the input video signal 9, the number of image density levels to be reproduced on the recording sheet 5, the exposure-density characteristic curve of the recording sheet 5, and the main scanning repetition frequency of the light beam on the recording sheet 5.
  • the signal thus subjected to analog-to-digital conversion is applied to a digital value collation circuit 16.
  • a signal corresponding to a read density of an input video signal is applied from the facsimile transmitter to the digital value collation circuit 16.
  • the digital signal thus applied is converted into a digital value representative of the number of pulses of a high frequency pulse signal as indicated in FIG. 2 by the digital value collation circuit 16.
  • zero to 1000 high frequency pulses are outputted as described above.
  • the collation value depends on the exposure-density characteristic of the recording sheet. Therefore, it is necessary to set the collation value in accordance with this characteristic of the recording sheet to be used.
  • the digital value collation circuit 16 can be implemented by a read-only memory for instance.
  • the digital value of the input video signal 9 is applied, as an address signal, to the circuit 16.
  • pulse numbers corresponding to applied address signals are outputted by the digital value collation circuit 16 with the timing of the sampling pulse signal.
  • the signal from the facsimile transmitter is expressed as a signal corresponding to a density which means that the signal has already been subjected to logarithmic conversion.
  • the logarithmic conversion operation may be included in the digital value collation circuit by appropriate choice of the digital values stored therein.
  • the high frequency pulse signal 12 is applied through an AND gate 17 to the clock input terminal of a counter 18.
  • the content of the counter 18 is cleared (or reset) by the sampling pulse signal 14 outputted by the sampling pulse generating circuit 13.
  • the output of the counter 18 is compared with the output of the digital value collation circuit 16 by a coincidence circuit 19.
  • the coincidence circuit 19 outputs a coincidence signal 20 of a logic "0".
  • the coincidence signal 20 is applied to the AND gate 17 to close the AND gate 17 thereby to block the high frequency pulse signal 12.
  • the coincidence signal 20 is further applied to an AND gate 21 to close the AND gate 21. Before the AND gate 21 is closed, the high frequency pulse signal 12 outputted by the high frequency oscillator 11 is applied through the AND gate 21 and the amplifier 22 to the semiconductor laser 1.
  • the sampling pulse signal 14 is applied to the AD converter 15 and the counter 18 again and the AD converter 15 converts the input signal into a digital value which is further converted into a digital value representative of the density by the digital value collation circuit 16 and the content of the counter 18 is once again reset. If, in this operation, the input signal is not zero, the coincidence circuit 19 outputs a signal 20 of a logic "1" indicating noncoincidence which is applied to the AND gates 17 and 21 to open the gates 17 and 21 as a result of which the high frequency pulse signal 12 is applied to the amplifier 22 and the counter 18. Thus, the high frequency pulse signal 12 is applied through the amplifier 22 to the semiconductor laser 1 until the coincidence circuit 19 again provides a coincidence signal 20 of "0".
  • the sampling pulse generating circuit 13 outputs a clock pulse signal 23 whose frequency is equal to that of the sampling pulse signal 14.
  • the clock pulse signal 23 is applied to the clock signal input terminal of a counter 24. The relation in phase between the sampling pulse signal 14 and the clock pulse signal 23 will be described later.
  • the counter 24 counts the pulses of the clock pulse signal 23 applied thereto and outputs a pulse of switching pulse signal 28, which may be a carry output of the counter 28, when the content of the counter 24 reaches a predetermined value.
  • the switching pulse signal 28 is applied to the sampling pulse generating circuit 13.
  • the output of the counter 24 is applied to a DA (digital-to-analog) converter 25 which in turn outputs a sawtooth wave signal 26 to drive a galvanometer 3.
  • the sawtooth wave signal 26 is applied through an amplifier 27 to the galvanometer 3 in response to which the galvanometer 3 deflects a laser beam 6 to form a scanning line 7 on the recording sheet 5.
  • FIG. 4 is a block diagram showing the sampling pulse generating circuit 13 in more detail and FIGS. 5 and 6 are timing charts for a description of the operation of the circuit 13.
  • the high frequency pulse signal 12 outputted by the high frequency oscillator 11 is applied to a frequency divider circuit 29 which in turn outputs the clock pulse signal 23.
  • the frequency division ratio of the frequency divider circuit 29 is 1000:1 because the frequencies of the high frequency pulse signal and the sampling pulse signal are 25 MHz and 25 KHz, respectively, as described above.
  • the clock pulse signal 23 is applied to the counter 24 to generate the sawtooth signal 26, as described before.
  • the clock pulse signal 23 is further applied to monostable multivibrators 30 and 32.
  • the monostable multivibrator 30, triggered by the fall of the clock pulse signal 23, outputs a pulse of a first sampling pulse signal 31.
  • the monostable multivibrator 32 is triggered by the rise of the clock pulse signal 23 in response to which it outputs a second sampling pulse signal 33.
  • the first and second sampling pulses signals 31 and 33 differ from each other only in phase with the phase difference being 180° in this embodiment. The above-described operations will become more apparent from the timing chart in FIG. 5.
  • the first and second sampling pulses signals 31 and 33 are supplied to a switching circuit 34 which selects and outputs one of the two sampling pulses as the sampling pulse signal 14 described above.
  • This sampling pulse selecting operation is controlled by the switching pulse signal 28 which is generated by the counter 24.
  • the pulses of the switching pulse signal 28 are outputted simultaneously when the counter 24 is cleared as described above, and therefore the switching of the first and second sampling pulse signals 31 and 33 is carried out by the switching circuit 34 for every main scanning line on the recording sheet.
  • the signals applied to the semiconductor laser 1 can be readily understood by referring to the timing chart of FIG. 7 which shows the relation among the high frequency pulse signal 12, the sampling pulse signal 14, the state of the AND gate 21 (indicated at a) and the high frequency pulse signal applied to the semiconductor laser through the AND gate 21 (indicated at b).
  • FIG. 8A shows the entire recorded image
  • FIGS. 8B-8E show various parts of the recorded image in larger scale. These parts have an intermediate densities.
  • each picture element of the recorded image is shown as a shadowed dot. In practice, the densities of the picture elements correspond to the input video signals.
  • FIGS. 8B and 8C show the picture elements as recorded when the invention is not employed, that is, in the case where the recording is carried out with the phase of the sampling pulse 14 maintained unchanged.
  • the dots are regularly arranged not only in the main scanning direction but also in the auxiliary scanning direction.
  • FIG. 8B illustrates the former case
  • FIG. 8C the latter case.
  • a secondary drawback is involved that the dots in the intermediate density part of the image are prominantly coupled to one another in the auxiliary scanning direction.
  • FIGS. 8E and 8D show arrangements of dots when the invention is employed. As is clear from a comparison of FIGS. 8E and 8D with FIGS. 8B and 8C, the secondary drawback due to the coupling of dots is eliminated and, accordingly, the image as a whole has a smooth texture.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Fax Reproducing Arrangements (AREA)
  • Exposure Or Original Feeding In Electrophotography (AREA)
  • Semiconductor Lasers (AREA)
  • Facsimile Image Signal Circuits (AREA)
US06/231,561 1980-02-08 1981-02-04 Laser recorder Expired - Lifetime US4370667A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP55/14627 1980-02-08
JP1462780A JPS56112175A (en) 1980-02-08 1980-02-08 Laser recording device

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4554561A (en) * 1983-04-11 1985-11-19 Xerox Corporation Multi-channel electro-optic printer for printing plural image lines at once
EP0241569A1 (de) * 1986-04-15 1987-10-21 Maurer Electronics Gmbh Bildwiedergabesystem zur Erzeugung eines digitalen Bildes
US4754291A (en) * 1986-02-24 1988-06-28 Fuji Photo Film Co., Ltd. Light beam scanning recording apparatus width modulation of both total pulse duration and intensity
EP0212990A3 (en) * 1985-08-29 1988-07-20 Canon Kabushiki Kaisha Image processing apparatus
US4870499A (en) * 1985-08-29 1989-09-26 Canon Kabushiki Kaisha Image processing apparatus
US4967211A (en) * 1988-06-14 1990-10-30 International Business Machines Corporation Printing machine with toner density balance in solid areas and line strokes
WO1991010311A1 (en) * 1990-01-04 1991-07-11 Eastman Kodak Company Non-impact print apparatus and method for grey level recording
EP0571167A2 (en) * 1992-05-21 1993-11-24 Xerox Corporation High addressability image generator using pseudo interpolation of video and screen data
EP0707412A3 (en) * 1994-10-11 1997-06-18 Seiko Epson Corp Method and apparatus for reducing artifacts in halftone error diffusion images using ink reduction processing
US6034787A (en) * 1991-05-20 2000-03-07 Canon Kabushiki Kaisha Image processing apparatus having a high gradation mode and a high resolution mode of operation

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3725574A (en) * 1971-02-18 1973-04-03 Method and apparatus for recording rastered continuous-tone pictures in printed graphics
US4001492A (en) * 1972-02-08 1977-01-04 Fuji Xerox Co., Ltd. Half tone reproducing process in facsimile
JPS55102966A (en) * 1979-01-30 1980-08-06 Matsushita Graphic Commun Syst Inc Half-tone reproduction circuit for facsimile or the like

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS588627B2 (ja) * 1975-03-03 1983-02-16 株式会社日立製作所 レ−ザ情報記録装置
JPS6056345B2 (ja) * 1978-03-23 1985-12-10 株式会社田村電機製作所 多階調画信号処理方式

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3725574A (en) * 1971-02-18 1973-04-03 Method and apparatus for recording rastered continuous-tone pictures in printed graphics
US4001492A (en) * 1972-02-08 1977-01-04 Fuji Xerox Co., Ltd. Half tone reproducing process in facsimile
JPS55102966A (en) * 1979-01-30 1980-08-06 Matsushita Graphic Commun Syst Inc Half-tone reproduction circuit for facsimile or the like

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
IBM Technical Disclosure Bulletin, vol. 18, No. 3, "Adaptive Contrast Ranging for Images", Wong, Aug. 1975, pp. 914-917. *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4554561A (en) * 1983-04-11 1985-11-19 Xerox Corporation Multi-channel electro-optic printer for printing plural image lines at once
EP0212990A3 (en) * 1985-08-29 1988-07-20 Canon Kabushiki Kaisha Image processing apparatus
US4870499A (en) * 1985-08-29 1989-09-26 Canon Kabushiki Kaisha Image processing apparatus
US4754291A (en) * 1986-02-24 1988-06-28 Fuji Photo Film Co., Ltd. Light beam scanning recording apparatus width modulation of both total pulse duration and intensity
EP0241569A1 (de) * 1986-04-15 1987-10-21 Maurer Electronics Gmbh Bildwiedergabesystem zur Erzeugung eines digitalen Bildes
US4967211A (en) * 1988-06-14 1990-10-30 International Business Machines Corporation Printing machine with toner density balance in solid areas and line strokes
WO1991010311A1 (en) * 1990-01-04 1991-07-11 Eastman Kodak Company Non-impact print apparatus and method for grey level recording
US6034787A (en) * 1991-05-20 2000-03-07 Canon Kabushiki Kaisha Image processing apparatus having a high gradation mode and a high resolution mode of operation
EP0571167A2 (en) * 1992-05-21 1993-11-24 Xerox Corporation High addressability image generator using pseudo interpolation of video and screen data
EP0571167A3 (en) * 1992-05-21 1994-01-26 Xerox Corporation High addressability image generator using pseudo interpolation of video and screen data
EP0707412A3 (en) * 1994-10-11 1997-06-18 Seiko Epson Corp Method and apparatus for reducing artifacts in halftone error diffusion images using ink reduction processing

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Publication number Publication date
JPS6363148B2 (ja) 1988-12-06
JPS56112175A (en) 1981-09-04

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